Sound actuated and producing device



Dec., 10, 1929.

L. DE FOREST SOUND ACTUATED AND PRODUCING DEVICE Filed oct. 29, 1926 /'S Strom/ms f-M) Patented Dec. 10, 1929 UNITED srarss PATENT OFFCE LEE DE FOREST, OE NEW YORK, N. Y., ASSIGNOB, BY MESNE ASSIGNMENTS, TO GENERAL TALKING PICTURES CORPORATION, A CORPORATION `OE DELAWARE SOUND ACTUATED AND PBODUCING DEVICE Application nled October 2Q, 1926. Serial No. 144,876.

My invention relates to microphones and loud speaking devices. I

One of the objects of this invention is the production of a microphonic or loud speaking device designed especiall for use in electric recording of and repro ucing from sound records.

Another object of this invention is to provide a microphonic or loud speaking device, which utilizes a capillary boundary bet-Ween two liquids vof diierent density. A further object of this .invention is to utilize two different liquids in a capillary, one which wets and one which does not wet the capillary, to

` produce a device mentioned above. A further object of this invention is the utilization of differences in potential across a meniscus of di-similar liquids within a capillary enve o Another object of this invention is the association of a device of this type with an input circuit to provide an operating connection with any type of output circuit or amplifier, such as a transformer, three electrode vacuum device and the like.

These and many other objects are successfully sought by the apparatus disclosed herein employing the principles of my invention.

This invention resides substantially in the combination, construction, arrangement and relative location of parts, as will appear more fully hereinafter.

Referring to -the drawings, Fig. 1 is a crosssectional view of one form of my device and an associated circuit.

Fig. 2 is a somewhat modified form of my device, employing the principle of my invention connected to a different form of amplifying device.

Fig. 3 is a further modification of my inL vention.

Fig. 4 is a vertical cross-sectional view taken at right angles to the views in Fig. 3, with the horn broken away.

Fig. 5 is a cross-sectional view of the container or envelope used in the construction of Figs. 3 and 4, showing more clearly the arrangement ofthe parts; and

Fig. 6 is a cross-sectional view of a still further modification of my invention, with its associated circuits.

It 1s a well known physical principle that when two dis-similar llquids, suchas mercury.

and dilute acid, are contained in the same capillary tube, a meniscus or semi-globular surface forms the boundary between the two liquids. When a small electromotive forcevis passed across this meniscus, from one liquid to the other, there results thereby a change in surface tension in the meniscus, which results in a sudden movement thereof, up or down, in the capillary tube. The movement of this meniscus is proportional to the amount of variation in the electromotive force and is assed across the contact surface conversely. en a constant electromotive force is im'- pressed across this contact surface any variation in the electromotive force will cause a movement of the meniscus. The Lippman electrometer is one form of the device, known to physicists, which employs the principles pointed out above. I have found that with some adaptions this principle may be used` -is likewise, true that if a varying electromotive force is applied across the contact surface of two dis-similar liquids within a capillary, the contact surface or meniscus will vary its position within the tube by and in accordance `With the differences of electromotive force across it to produce sound waves.

Referring to the drawings, as shown in Fig. 1 a capillary tube 1 is closed with a small bulb, at one end, and diverging upwardly at the other end to form a conical horn. A liquid which does not wet the tube, such as mercur is shown at 4 and a dis-similar liquid which oes wet the tube, a capillary, such as dilute acid is shown at 5. A meniscus is as a loud speaker or a microphone. p

formed at the surface of contact between the two liquids as shown at 6. .A termlnal 6 is shown in contact with the liquid 5, and a terminal 7 is shown in contact with the li uid 4.v

A small air` space is formed in the bul 2 by reason of the ltrapped air therein. A lead from the terminal 6 is connected to one end of' a resistance 10, to one terminal of a condenser 12 and to one terminal of a battery 11. The other terminal of the battery is connected to the other end of the resistance 10, and the other terminal of thecondenser 12 is connected in series' to the primaryA 8 of a transformer connected in turn to the terminal'?. A movable contact and connection is also made from some terminal of the condenser and is adapted to contact with the resistance. It will be noted that this arrangement provides a well known potentiometer. A secondary of the transformer 9 may be connected to any suitable in ut or out ut circuit depending upon whet er the devlee is to be used A somewhat similar arrangement is shown in Fig. k2, where the tube 1is provided with an open end'2 and the. other end diverging intuhthe horn 3. The two liquids 4 and 5 are shown having the terminals V7 and 6, respectively. As before, the curved surface of contact 5 is formed between the li ids. In this case the lead from the terminal a lead from tube 18.

the battery 11 and one end of the resistance 10 are connected together. The other terminal of the battery 11 is lconnected to the other end of the resistance 10, and the variable contact 13 is connected to one end of a resistance cou ling 14, one terminal of the battery 17,

anr the filament of a three electrode vacuuml The wire fromthe terminal 6 isl nected to be used as a micro hone.l The condenser 15 is a stopping con enser'to keep the current from the battery 17 lfromfiowingl directly through the two li uids. The resist-` ance 14 provides the well own type of resistance cou ling and the resistance 16 acts as a, grid lea The modified form shown in Figs. 3, 4

- `and 5 comprises an insulating envelo e 20 o any material, to which is connected a orn or other suitable sound collecting or directing horn 21. Within the envelope are supported a plurality of insulating latese25 rovided with holes 27 therethroug One o the liquids, such as mercury, shown at 22 on top of ,producin sound which floats a lighter liquid, such as dilute acid, and a thin film of oil 24 is supported thereon to prevent evaporation. A terminal 26 connects to the upper liquid and a terminal 27 connects to a lower liquid. The holes 27 are provided. to insure an even distribution of the mercury between all the plates.

It will be noted that in thisvr arrangement instead of having only one meniscus surface of contact, there are a large number of them, that is one between each two adjacent plates. B means of thisarrangement a much'greater e ect is produce the forms in Figs. 1 and 2.

A modified form is shown in Fig. 6 invwhich thel insulating envelope 30 contains dilute acid 32. An adjustable thumb screw 33-is provided at its lower end with a short length of fine wire 34, such as Wollaston wire, whi ch contacts lightly with the liquid. .A thin film of oil may be disposed upon the solution to .prevent evaporation when desirable. The

i wire 35 is in contact with the lower liquid,

and is connected to one end of the resistance 36 and one terminal of the battery 38. The other terminal of the resistance 36 is connected to the other terminal of the battery. 38. A wire leads from the thumb screw 33 to one terminal of the primary 39 of the transformer, the other end of which is connected to a movable contact 37, which cooperates with the resistance 36. The secondary 40 of the transformer provides the output circuit when the device is used as a micro hone.

It will be seen from the foregolng description that I have provided several vforms of apparatus suitable for beine` actuated by or waves emlloying the rinciples whichl I carefully pointed out a ove. above.

With an arrangement, such as I have devscribed I obtain a novel and very satisfactory loud speaker. If tliel meniscus surfaces are small enou h, or in other words, if the mass of the liqui sin the ca illary or in the narrow space between the a 'acent plates is suiiiciently small, a slight c ange in applied electromotivefor'ee across the contact'surfaces produces a relatively large displacement thereof with corresponding displacement of the acidulated water of such surface, up or down, as the case may be in accordance with the reversals of the applied electromotive than would be secured from force. There is no appreciable lag to this device for electrical frequencies, such as are involved in sound reproduction. The air above the acidulated water is thereby subjected to very rapid -alternating com ression and rarefaction resultin lin soun waves vhich are forced out of t e sound directing orn.

One of the valuable features of a device of this type is that it. has no natural period of vibration corresponding to a natural period of resonance of the diaphragm or armature system of the ordinary electromagnetic sound device, and I have found that the device is non-selective over a wide range of frequencies.

I do not desire to be limited to the particular constructions and arrangements shown and described for. purposes of illustration.` For instance, I do not desire to be limited to the particular4 liquids disclosed b me as suitable, since it is possible lthat ot er dissimilar liquids may readily be employed.

I do not desire to be `limited to the particular mechanical forms of the device, nor i with the materials used to construct them, and in fact I contemplate any form of device employing the principles of this invention, which would occur to those skilled in the art. I further do not desire to be limited to the -particular circuits which I have associated with the device since many other arrangements and combinations of circuit elements may be used in conjunction with my novel device.

I do not, therefore, desire to be limited to the illustrative embodiments of my invention, but rather to the spirit and scope there of as I deine them in the appended claims.

hat I seek to secure by United States Letters Patent is 1. In a sound reproducing device of the type described, an elongated container having a relatively small cross section, said contamer having an enlarged conical portion at one end forming a horn, two liquids'of' different density in surface contact in said container at least one of'said liquids bein open to the atmosphere through said conica portion, a terminal in each li uid and means for impressing varyin electrical currents on said terminals to pro uce sounds in accordance with the varying electrical currents causing physical displacement of the liquids in said container whereby the atmosphere in contact therewith is subjected to rarefactions and compressions.

2. In a sound reproducing device of the -t e described, a container having a ortion t ereof enlarged to form a horn, two quids of different .densities in surface contact within the container, means for confining the two liquids into at least one bod of small cross sectioned area, the body of 'quid bein exposed to the atmos here through said orn, a terminal in each iquid and means for impressing varying electrical currents on the terminals to produce sounds by the varying aceelectrical currents causing physical disp ment of the liquids in said container whereby the atmosphere in contact therewith is subj ected to rarefactions and compressions.

`3. In a sound reproducing device of the type described, a. container having a portion thereof enlarged to form a horn, two liquids of different densitiesl in surface contact within the container, means for confining tle two liquids into at least one body of small cross sectional area, the body of liquid being exposed to the atmosphere through said horn, a terminal in each llquid, external means for maintainin a difference of potential across the terminzils and means forv varying the potential across said terminals by and in accordance with speech currents to cause displacement of said liquids resulting in the production of sound waves.

4. In a device for reproducing sound from electrical currents which comprises a container having at least one portion of ca illary cross section and a portion forme to rovide sound directing means, two immiscile conducting fluids in surface contact at the portion of capillary cross section, a plurality of terminals in respective contact with each of said liquids whereby when varying potentials are impressed across said terminals the currents flowing across said surface of contact cause electro-physical displacements of the liquid with a resultant production of sound waves.

In testimony whereof I have hereunto set my hand on this 25th day of Oct., A. D. 1926. 9o

LEE DE FOREST. 

